Powdered iron magnetic core



w April 29, 1947' A. F. MITT'ERMAIER -2,419,847

POWERED IRON MAGNETIC CORE Filed June 2. 1944 Figi Patente Apr. 29, 1947 UNITE STATES PA FFMIE or to General Electric of New York Company, a corporation Application June 2, 1944, Serial No. 538,482

My invention relates to powdered iron bonded magnetic cores, and to an improved method of making such a core.

It has been customary to form electromagnetic cores particularly for high frequency application of powdered iron which is bonded together with suitable material,l such as a phenolic condensation product, varnishes, chrome silicate, and waxes. The iron particles have also been insulai'ed from each other -by mixing the powdered iron with an insulating material such as clay before the powder is bonded together with a bindcr. Cores which I formed according to past practice, however, by the use of high pressure had relatively high core losses and were not consistent in electrical characteristics.

It is therefore an object of my invention to provide an improved powdered iron bonded core.

Another object of my invention i-s to provide an improved method of forming a. powdered iron bonded core. i

Further objects and advantages of my Invention will 'become apparent from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the ciaims annexed to and forming a part. of this specification.

In the -drawing, Fig. 1 illustrates a mold apparatus in which my iniproved core is formed; Fig. 2 illustrates a core produoed in the mold of Fig. 1; Fig. 3 iilustrates a. modified mold construction for producing a mcdification of the core illus'- trated in Fig. 2, and Fig. 4 illustrates the core produced in the mold of Fig. 3.

My improved core is formed by mixing powdered iron of suitable fineness with a suitable insulating material such as clay. The clay is employed so as to prevent relative high eddy currents, but if the eddy currents are not material the clay or similar insulating material may be omitted. The mixture of powdered iron and clay is then mixed with any suitable heat hardenable substantiaily solventless liquid binding material such as esters of saturated monohydric alcohols and unsaturated monob'asic carboxylic acid. Further examples of such materials are given in applications for Nordlander and Hargraves, S. N. 302,164, and Nordlander, S. N. 302,165 and S. N. 302,166. These further examples are listed below as follows:

Polymerizable comDOsitions comprising (1) a polymerizable polyhydrlc 'alcohol ester of an s oiaims. (ci. 175-121) alpha-unsaturated alpha, beta-polycarboxylic acid, e. g., diethylene glycol maleate, diethylene glycol fumarate, etc., and (2) a polymeriable monohydric alcohol ester oi' an alpha-unsaturated alpha,beta-polycarboxylic acid, e. g., diethyl fumarate, dipropyl itaconate, diallyl maleate, diallyl itaconate, etc.

Polymerizable compositions comprising (1) a polymerizable 4polyhydric alcohol ester of an alpha-unsaturated alpha,beta-polycarboxylic acid and (2) a polymerlza'ole polyester obtained by esterifying an aromatic polycarboxylic acid or anhydride with. an unsaturated monohydric alcohol, e. g., diallyl phthalate.

Polymerizable compositions comprising (1) a polymerizable polyhydric alcohol ester of an alpha-unsaturated alpha,beta-polycarboxylic acid and (2) and .an unsaturated monohydric alcohol triester of a tribasic acid, specically triallyl phosphate, trialiyl citrate, triailyl tricarballylate or triallyl aconitate. y

In order to prodiice a. core which will not ice ruhbery, ii have found it is desirable to use a suitaloie moimt o eatalyst with the solventless bon' .terial, is, about 3 per cent by Weight of total a ;cant of bonding material emplofeitl. ;any r' catalyst may be empioyed such e such as benzoyl peroxidc. Any lens of powdered iron insulation material soiyentless binder may be employed and I have found that a mixture including about 8 parts of ciay, 66 parts iron, and 26 parts binder produces a very desirable core.

In Fig. 1 I have illustrated somewhat diagrammatically a mold having similar portions i and ll which fit into a base 2, in' which mold 'the materials described above may be poured from a vessel |3 to produce a core. In order to insure that the mixture will fill all parts of the mold, the mixture is preheated before introducing into the mold to a temperature just below the polymerization temperature of the resin binder, and for the materials mentioned above the mixture is heated to about degrees C. for about 5 minutes while it is being agitated. The mixture is then poured into the mold to produce the core. Sin order to pre'vent the mixture from chilling when it is poured into the mold, the mold is preheated to at least the temperature that the mixture has, such as around, to degrees by the use of heating coils H and 15. The mold is maintained at the temperature of about 100 degrees for a few minutes and then raised to above the polymerization temperature of the binder, such as being raised to about 130 degrees for a suitable time such as 1 hour. After the mold has cooled the two halves and li may be disassembled leaving 9, core |6 as is illustrated in Fig. 2.

I have found that the resulting core formed in the manner described above has better electrical characteristics than a similar core formed of powdered iron bonded together with chrome silicate. Tests of such cores were made by connecting the primary of a transformer having the powdered iron core in series with a capacitance to form a series resonant circuit and the highest voltage induced in the secondary winding of the transformer which also surrounded the core was measured. The transformer core having the powdered iron bonded together with chrome silicate was formed by mixing 300 mesh powdered iron with sufiicient chrome silicate, the core being hardened under heat and pressure. A transformer having such a core when tested in the resonant circuit described above had a maximum induced voltage in the secondary of about 10,000 volts, while a transformer having a core formed according to my invention with a similar amount of powdered iron had a maximum induced voltage in the secondary of about 18,000 volts. It will be appreciated that the difference in voltages is a. measure of the relative eflioiencies of the two types of cores, and my imprcved core was therefore considerably more eficient.

Not only will my improved core have efflcient electrical characteristics, but by casting the ingredients in the manner described above, suitable slots il may be placed in the outer surface of the core for the reception of a winding such as the low voltage primary winding turns. It will be seen that the mold -sections 10 and ll have their inner surfaces suitably slotted so as to produce the winding slots in the outer surface of the core, as is illustrated in Fig. 2. If winding slots are desired in a powdered iron core formed according to past practice by the application of pressure,

not only is a much more electrically ineflicient core produced but the core will be formed first with a cylindrical surface, after which the core is machined to produce the Slots, and unless the powdered iron is bonded very solidly together the ridges 'between the slots may crumble.

A winding if desired may be cast into the core formed according to my invention, and in Fig. 3 I have illustrated a mold having portions 18 and |9 filled with a mixture of iron, clay and solventless binder, as is described above. 'I'he mixture is, of course, heated and before it hardens a winding 20 is inserted so as to be cast into the core. Insteacl of introducing the winding 20 into a heated mixture in the mold, the winding may be previously inserted in the mold and then the mixture poured in and then polymerized around the winding. Fig. 4 illustrates a core 2| forzned with the winding 20 cast therein.

Although I have shown and described particular embodiments of my invention, I do not desire to be limited to the particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What 1 claim as new and desire to secure by Letters Patent of the United States is;

1. A mechanically strong uncompressed magnetic core material comprising particles of powdered magnetic material bonded together by a polymerized alcohol ester of carbonlic acid.

2. A hard mechanically strong pressure free low loss magnetic core casting comprising a mixture of powdered magnetic material and powdered insulating material bonded together by a polymerized polyhydrio alcohol ester of an alphaunsaturated alpha,beta-polycarboxylic acid and a catalyst.

3. A hard mechanically strong gravity compacted low loss magnetic core casting comprising, by weight, substantially 66 parts powdered iron, 26 parts binder and 8 parts clay, said binder comprising, by weight, substantially 97 parts polymerized polyhydric alcohol ester of alphaunsaturated alpha,beta-polycarboxylic acid and 3 parts catalytic peroxide.

4. A hard mechanically strong gravity compacted low loss magnetic core casting comprising, by weight, substantially 66 parts powdered. iron, 26 parts binder and 8 parts clay, said binder comprising, .by weight, substantially 9'7 parts polymerized polyhydrlc alcohol ester of an alphaunsaturated alpha,beta-polycarbowlic acid and a polymerizable monohydric alcohol ester of an alpha-unsaturated alpha,beta-polycarboxyllc acid and 3 parts benzoyl peroxide as a Catalyst.

5. A hard mechanlcally strong gravity compacted low loss magnetic core casting comprising, by weight, substantially 66 parts powdered iron, 26 parts .binder and 8 parts clay, said binder comprising, by weight. substantially 97 parts polymerized polyhydric alcohol ester of an alphaunsaturated alpha,beta-polycarboiwlic acid and a polyester obtained by esterifying an aromatic polycarboxylic acid or anhydride with an unsaturated monohydric alcohol and 3 parts benzoyl peroxide as a Catalyst.

6. A hard mechanically strong gravity compacted low loss magnetic core casting comprising, by weight, substantially 66 parts powdered iron, 26 parts binder and 8 parts clay, said binder comprising,` by weight, substantially 97 parts polymerized polyhydrio alcohol ester of an alphaunsaturated alpha,beta-polycarboxy1ic acid and an unsaturated monohydric alcohol triester of a tribasic acid and 3 parts benzoyl peroxide as a Catalyst.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'I'ENTS Number Name Date 2,230,228 Bandur Feb. 4, 1941 1,982,689 Polydorofi Dec. 4, 1934 2,273,891 Pollack et al. Feb. 24, 1942 2,195,362 Ellis Mar. 26, 1940 1,867,362 Lathrop July 12, 1932 1,881,711 Iratljirop Oct. 11, 1932 2,043,3i6`''I 'Buckley June 9, 1936 2,330,590 Kaschke Sept. 28, 1943 1,948,308 Neighbors Feb. 20, 1934 1,994,534 Robinson Mar. 19, 1935 FOREIGN PA'I'EN'IfS Number Country Date 647,072 French July 24, 1928 

